1. Field of Use
The present invention relates to apparatus for converting AC voltages to relatively low level DC voltages and more particularly to switching regulator power supply apparatus.
2. Prior Art
In general, computer equipment and associated peripheral equipment include their own internal power supplies. Such supplies are used to convert AC line voltages having the voltage ranges of 95-132 volts and frequencies of 50-60 Hertz into required DC voltages of 5-24 volts. In operation, these supplies generally have the AC line voltages applied to the primary windings of a step down transformer. The voltages induced in the secondary windings of the transformer are rectified, filtered and averaged to obtain the desired values of DC voltages.
As computer equipment and peripheral equipment become more compact and smaller in size, it becomes necessary to reduce the size weight and power requirements of the internal power supplies utilized therein. One approach has been to reduce the complexity of the high frequency switching circuitry associated with primary windings of the transformer. Examples of this approach are illustrated in U.S. Pat. Nos. 3,924,172, 4,005,790 and 4,128,867.
While the arrangements described in the above patents reduce the circuit complexity in this part of the power supply, the arrangements normally require additional circuitry which include separate line frequency transformers which power the control pulse circuits connected between the primary and secondary transformer windings. These arrangements may also include feedback circuits which couple to the line frequency transformer or bias transformer and circuits for providing power to operate the control circuitry during power supply operation.
Another approach is to employ a transformer flyback arrangement which utilizes a clock circuit which couples to the AC line power circuits through voltage doubling circuits. The clock circuit operates to generate a variable width pulse at a fixed frequency which is applied to power switching circuits which couple to the primary winding of the transformer. During the time interval defined by the width of the clock circuit pulse, the power switching circuits deliver power to the primary windings. At the end of the interval, the power switching circuits turn off causing current flow in the opposite direction through primary winding (transformer flyback). This induces a voltage in the secondary windings of a polarity which permits the transfer of energy to a load. At the end of this transfer cycle which occurs during transformer flyback defined by the fixed frequency of the clock circuit, another energy storage cycle is initiated. An amplitude pulse width converter compares the voltage output of the power supply with predetermined value and a feedback circuit DC couples signals from the converter for shortening the duration of the energy storage cycle by shortening the pulse width. An example of this type of arrangement is described in U.S. Pat. No. 4,001,663.
The above type of arrangement has been found to be quite complex due to the additional circuits required for furnishing power to the clock circuit and controlling the pulse width. More importantly, it has been found that such an arrangement cannot be easily controlled so as to minimize power supply consumption.
Accordingly, it is a primary object of the present invention to provide a light weight, compact and efficient power supply.
It is a further object of this invention to provide a switching regulator power supply which minimizes power consumption and maximizes energy transfer notwithstanding changes in input line voltage.
It is still a further object of the present invention to provide a switching regulator power supply which is easily constructed in integrated circuit form.